This invention relates to multistage hydraulic machines, and more particularly to apparatus for cooling areas of a multistage hydraulic machine developing high heat between rotary and stationary elements of the machine.
Often a multistage hydraulic machine involving a pump-turbine is used to generate electricity during the day and pump water from a lower level to a higher level during the night, that is, during periods in which the demand for electricity is not high. By supplying pressurized air in a runner chamber, the water is exhausted from the water passageway after an electricity generation cycle and before a pump cycle to avoid high load on the runners in starting up the pumping operation. During this phase modification the runners may be rotated in air for a considerable period of time and high frictional heat develops between the rotary and stationary elements of the machine.
Consequently, the runners will become larger because of thermal expansion and the seal gaps between the rotary elements, such as peripheral edges of the runner, and the stationary elements, such as a head cover, a bottom ring and a return ring, will become smaller. The rotating runners may even contact the stationary elements and be damaged.
In order to avoid possible contact between the runner and the stationary elements, cooling water is ordinarily supplied to the runner seal gap, that is, between the peripheral portion of the runner and a liner of the bottom ring. By supplying the cooling water, the runner is cooled and the seal gap is kept open. In the case of a monostage hydraulic machine, it is easy to provide a supply pipe for supplying the cooling water to the runner seal portion, because there is a concrete foundation, under the bottom ring, through which the cooling water can flow.
However, in the case of a multistage hydraulic machine, the return passages of a plurality of the runner chambers are connected serially, so that this hydraulic machine has a complicated water flow passage. It is more difficult to supply cooling water to a runner seal portion at a higher-pressure stage than to a lower-pressure stage of the water flow passage. Accordingly, it has not been possible in the prior art to cool high friction areas of a multistage hydraulic machine adequately when it is occupied in changing over from electricity generation to pumping water or during a condenser operation, and the runners are operating in air for a considerable period of time.